1. Field of Invention
The present invention relates to a resonant wireless power receiver circuit, particularly, to a resonant wireless power receiver circuit with a bridge rectifier circuit. The present invention also relates to a control circuit and a resonant wireless power conversion method.
2. Description of Related Art
FIG. 1 shows a prior art resonant wireless power receiver circuit 1. The resonant wireless power receiver circuit 1 comprises a resonant circuit 31, a bridge rectifier circuit 33, a DC-DC converter 34 and a load 35.
The wireless power transmission is achieved as thus. In FIG. 1, a resonant wireless power transmitter circuit (not shown) transmits a wireless power 40 to a wireless field (for example but not limited to a magnetic field, an electric field or an electromagnetic field). The wireless power 40 in the wireless field is received by the resonant wireless power receiver circuit 1 with the resonance effect of the resonant circuit 31 through for example but not limited to coupling, induced by, or capturing the wireless power 40 in the wireless field. A resonant output voltage VAC is generated at an output of the resonant circuit 31. The rectifier circuit 33 rectifies the resonant output voltage VAC to generate a rectified output voltage VRECT which is then converted by the DC-DC converter 34 to generate an output voltage VOUT to drive the load 35.
The prior art in FIG. 1 has a drawback that the rectified output voltage VRECT may be too low or too high. And, due to the uncertain level of the rectified output voltage VRECT, an extra regulation circuit (e.g. DC-DC converter 34) is required to generate a stable output voltage.
Since the operation of the prior art shown in FIG. 1 is based on resonance effect, if the resonant frequency transmitted by the resonant wireless power transmit circuit drifts from its preset frequency, or if the receiver circuit is not properly located at a proper relative distance and a proper relative angle, or if there are multiple resonant wireless power receiver circuits coupled to receive the wireless power at the same time, off resonance could happen. If the off resonance is not corrected or controlled, it could cause power loss, or the received voltage (for example the resonant output voltage VAC and the rectified output voltage VRECT) could be too low such that circuits at the following stage (such as the DC-DC converter 34 and the load 35) cannot function properly.
FIG. 2 shows a Bridge Doubler Rectifier according to a prior art rectifier circuit disclosed by U.S. Pat. No. 4,268,899. When CR5 is not conductive, the Bridge Doubler Rectifier operates in 1× voltage mode, and when CR5 is conductive, it operates in 2× voltage mode. The prior art in FIG. 2 has the following drawbacks: (A) it requires two output capacitors connected to each other in series, so the equivalent capacitance is half of that of a single capacitor; (B) CR5 has to be a bi-directional control switch; (C) there are only two options for its output voltage, nevertheless as mentioned previously, since the power received by the resonant wireless power receiver circuit with resonance effect is uncertain, the output voltage generated by the prior art rectifier may be too low in 1× mode and too high in 2× mode, i.e., neither 1× nor 2× is proper, which may lead to malfunction or damage of circuits in its following stages.
FIGS. 3A and 3B show another prior art resonant wireless power receiver circuit. The resonant wireless power receiver circuit 2 includes a 1×/2× active rectifier 38 (the details thereof are shown in FIG. 3B). The 1×/2× active rectifier 38 can rectify the wirelessly received AC voltage to a selectable one time (1×) or two times (2×) rectified output voltage to solve the aforementioned low output voltage problem of the rectifier.
However, the prior art circuits shown in FIG. 3A-3B have the following drawbacks. First, the circuit of 1×/2× active rectifier 38 is very complicated and needs a large number of devices. Second, there are only two options for the output voltage. However, as described in the above, the level of the resonant power received by the resonant wireless power receiver circuit 2 is uncertain, and it is possible in certain circumstances that 1× is too low while 2× is too high, such that the circuits of the following stages either cannot function normally or are damaged.
Compared to the prior art in FIG. 1, the present invention has an advantage that the rectifier output is feedback controlled, such that the output voltage of the rectifier circuit is not too high nor too low. Another important advantage is that, since the present invention provides a stable rectifier output voltage or current, the DC-DC converter can be omitted, which greatly reduces the cost.
Compared to the prior art in FIGS. 2, 3A and 3B, the present invention has an advantage that the rectifier output is adjustable in a continuous way, such that the output voltage of the rectifier circuit is not too high nor too low. Another advantage is that the present invention can operate with less components and can share inherent components of the original rectifier circuit, so the present invention can reduce the manufacture cost.